Birefringent interlayer for attenuating standing wave photoexposure of a photoresist layer formed over a reflective layer

ABSTRACT

A method for attenuating within a microelectronics fabrication a standing wave photoexposure of a photoresist layer formed upon a reflective layer, and a microelectronics fabrication employed within the method. To practice the methods there is first provided a substrate employed within a microelectronics fabrication. There is then formed over the substrate a reflective layer. There is then formed upon the reflective layer a birefringent material layer. The birefringent material layer attenuates a standing wave photoexposure of a photoresist layer subsequently formed upon the birefringent material layer, where the photoresist layer is subsequently photoexposed with an actinic photoexposure radiation beam.

This is a division of patent application Ser. No. 08/868,845, filingdate Jun. 9, 1997, now U.S. Pat. No. 5,945,255 issued Aug. 31, 1999Birefringent Interlayer For Attenuating Standing Wave Photoexposure Of APhotoresist Layer Formed Over A Reflective Layer, assigned to the sameassignee as the present invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to photolithographic methods andmaterials employed within microelectronics fabrications. Moreparticularly, the present invention relates to photolithographic methodsand materials employed in attenuating standing wave photoexposures ofphotoresist layers formed upon reflective layers employed withinmicroelectronics fabrications.

2. Description of the Related Art

Integrated circuit microelectronics fabrications are formed fromsemiconductor substrates within and upon whose surfaces are formedresistors, transistors, diodes and other electrical circuit elements.The electrical circuit elements are connected internally and externallyto the semiconductor substrate upon which they are formed throughpatterned conductor layers which are separated by dielectric layers.

As integrated circuit microelectronics fabrication technology hasadvanced and integrated circuit microelectronics fabrication devicedimensions have decreased, several novel effects have become morepronounced within the methods and materials through which are formedadvanced integrated circuit microelectronics fabrications. Inparticular, within the photolithographic methods and materials throughwhich are formed patterned layers and patterned structures withinadvanced integrated circuit microelectronics fabrications, a significantnovel effect which has evolved is the standing wave photoexposure effectby which actinic photoexposure radiation employed in photoexposingphotoresist layers formed upon reflective layers within advancedintegrated circuit microelectronics fabrications is reflected back fromthose reflective layers and into those photoresist layers in a fashionthrough which there is provided an inhomogeneous standing wavephotoexposure of those photoresist layers. A pair of schematiccross-sectional diagrams illustrating the results of progressive stagesin forming a pair of inhomogeneously standing wave photoexposedpatterned photoresist layers upon a reflective layer within an advancedintegrated circuit microelectronics fabrication is shown in FIG. 1 andFIG. 2.

Shown in FIG. 1 is a substrate 10 having formed thereover a blanketreflective layer 12 which in turn has formed thereupon a blanketphotoresist layer 14. As shown within FIG. 1, the blanket photoresistlayer 14 is photoexposed through a photoexposure reticle 16 whileemploying an actinic photoexposure radiation beam 18, where portions ofthe actinic photoexposure radiation beam 18 within the blanketphotoresist layer 14 are reflected back from the surface of the blanketreflective layer 12 and into the blanket photoresist layer 14, thusyielding a standing wave photoexposure within the blanket photoresistlayer 14.

Shown in FIG. 2 is the results of developing the photoexposed blanketphotoresist layer 14 illustrated in FIG. 1. Shown in FIG. 2 is a pair ofstanding wave photoexposed patterened photoresist layers 14a and 14bformed upon the blanket reflective layer 12, where due to the standingwave photoexposure of the blanket photoresist layer 14 the standing wavephotoexposed patterned photoresist layers 14a and 14b have irregularlyformed sidewalls. As is understood by a person skilled in the art,although FIG. 1 and FIG. 2 illustrate the blanket photoresist layer 14and the pair of standing wave photoexposed patterned photoresist layers14a and 14b as implicitly formed from a positive photoresist material,photoresist layers analogous to the blanket photoresist layer 14 asshown in FIG. 1 and the standing wave photoexposed patterned photoresistlayers 14a and 14b as illustrated in FIG. 2 may also be formed whenemploying a blanket photoresist layer formed from a negative photoresistmaterial. Standing wave photoexposed patterned photoresist layers, suchas the pair of standing wave photoexposed patterned photoresist layers14a and 14b as illustrated in FIG. 2, are undesirable within advancedintegrated circuit microelectronics fabrications since there is oftenformed when employing those standing wave photoexposed patternedphotoresist layers patterned integrated circuit layers and patternedintegrated circuit structures with compromised dimensional integrity.

It is thus towards the goal of providing photolithographic methods andmaterials through which there may be attenuated standing wavephotoexposures of photoresist layers formed upon reflective layerswithin microelectronics fabrications that the present invention isgenerally directed.

Various methods and materials have been disclosed in the arts ofmicroelectronics fabrications for providing novel optical structureswithin microelectronics fabrications or for addressing novel opticalconsiderations within microelectronics fabrications. For example,Doorman, et al., in U.S. Pat. No. 4,849,080 discloses a method formanufacturing an optical stripline waveguide for non-reciprocal opticalcomponents within microelectronics fabrications. The method employsforming a surface lattice disordered waveguide strip material surroundedby an iron garnet cladding material, where the iron garnet claddingmaterial has an index of refraction less than the index of refraction ofthe surface lattice disordered waveguide strip material.

In addition, Tsujita, in U.S. Pat. No. 5,547,813, discloses a method forforming within a microelectronics fabrication a fine photoresist patternof high resolution while employing a contrast enhancement layer. Themethod employs a spacer layer of index of refraction 1.3 to 1.4separating the contrast enhancement layer from a photoresist layer fromwhich is formed the fine photoresist pattern, where the thicknesses ofthe contrast enhancement layer and the spacer layer are furtherco-specified.

Most pertinent to the present invention, however, is Lur et al., U.S.Pat. No. 5,580,701, who disclose a method for eliminating a standingwave effect when photoexposing a photoresist layer formed upon areflective layer within a microelectronics fabrication. The methodemploys an anti-reflective interference stack layer interposed betweenthe photoresist layer and the reflective layer, where the relativeindices of refraction of the materials from which are formed thephotoresist layer, the anti-reflective interference stack layer and thereflective layer are further co-specified.

Desirable in the art are additional photolithographic methods andmaterials through which inhomogeneous standing wave photoexposures ofphotoresist layers formed upon reflective layers within microelectronicsfabrications, such as but not limited to integrated circuitmicroelectronics fabrications, may be attenuated. It is towards thisgoal that the present invention is more specifically directed.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide aphotolithographic method for attenuating within a microelectronicsfabrication an inhomogeneous standing wave photoexposure of aphotoresist layer formed upon a reflective layer.

A second object of the present invention is to provide a method inaccord with the first object of the present invention, where themicroelectronics fabrication is an integrated circuit microelectronicsfabrication.

In accord with the objects of the present invention there is provided bythe present invention a method for attenuating within a microelectronicsfabrication an inhomogeneous standing wave photoexposure of aphotoresist layer formed upon a reflective layer. To practice the methodof the present invention, there is first provided a substrate employedwithin a microelectronics fabrication. There is then formed over thesubstrate a reflective layer. There is then formed upon the reflectivelayer a birefringent material layer. Finally, there is formed upon thebirefringent material layer a photoresist layer which is subsequentlyphotoexposed employing an actinic photoexposure radiation beam.

The present invention provides a photolithographic method forattenuating within a microelectronics fabrication an inhomogeneousstanding wave photoexposure of a photoresist layer formed upon areflective layer. The method of the present invention realizes thisobject by employing a birefringent material layer formed interposedbetween the photoresist layer and the reflective layer within themicroelectronics fabrication.

The present invention may be employed where the microelectronicsfabrication is an integrated circuit microelectronics fabrication. Themethod of the present invention does not discriminate with respect tothe nature of the microelectronics fabrication within which is formedthe photoresist layer, the birefringent material layer and thereflective layer. Thus, although the method of the present invention ismore likely to provide value for advanced integrated circuitmicroelectronics fabrications which employ diminished dimensions, themethod of the present invention may be employed within microelectronicsfabrications including but not limited to integrated circuitmicroelectronics fabrications, solar cell microelectronics fabrications,ceramic packaging microelectronics fabrications and flat panel displaymicroelectronics fabrications.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention areunderstood within the context of the Description of the PreferredEmbodiment, as set forth below. The Description of the PreferredEmbodiment is understood within the context of the accompanyingdrawings, which form a material part of this disclosure, wherein:

FIG. 1 and FIG. 2 show a pair of schematic cross-sectional diagramsillustrating the formation of a pair of inhomogeneously standing wavephotoexposed patterned photoresist layers upon a reflective layer withina microelectronics fabrication in accord with a method conventional inthe art of microelectronics fabrication.

FIG. 3 to FIG. 5 show a series of schematic cross-sectional diagramsillustrating the results of progressive stages in forming within anintegrated circuit microelectronics fabrication a pair of patternedreflective conductor layers while attenuating an inhomogeneous standingwave photoexposure of a photoresist layer employed as an etch mask informing the pair of patterned reflective conductor layers, in accordwith a preferred embodiment of the method of the present invention.

FIG. 6 shows a graph of Relative Optical Power versus Distance IntoPhotoresist Layer determined through a prophetic computer simulation forattenuating standing wave photoexposure of a photoresist layer formedupon a reflective layer in accord with the preferred embodiment of themethod of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a method for attenuating within amicroelectronics fabrication an inhomogeneous standing wavephotoexposure of a photoresist layer formed upon a reflective layer. Themethod of the present invention realizes this object by forminginterposed between the photoresist layer and the reflective layer abirefringent material layer.

Although the preferred embodiment of the method of the present inventionillustrates the method of the present invention employed in attenuatingan inhomogeneous standing wave photoexposure of a blanket photoresistlayer formed upon a blanket reflective conductor layer within anintegrated circuit microelectronics fabrication, the method of thepresent invention may alternatively be employed in attenuatinginhomogeneous standing wave photoexposures within photoresist layersformed upon reflective layers other than reflective conductor layerswithin microelectronics fabrications other than integrated circuitmicroelectronics fabrications. In that regard, the method of the presentinvention may be employed in attenuating inhomogeneous standing wavephotoexposures within photoresist layers formed upon reflective layersincluding but not limited to reflective conductor layers, reflectivesemiconductor layers and reflective insulator layers formed withinmicroelectronics fabrications including but not limited to integratedcircuit microelectronics fabrications, solar cell microelectronicsfabrications, ceramic packaging microelectronics fabrications and flatpanel display microelectronics fabrications.

Similarly, as is also understood by a person skilled in the art,although the preferred embodiment of the method of the present inventionillustrates the method of the present invention employed in attenuatingwithin an integrated circuit microelectronics fabrication a standingwave photoexposure of a blanket photoresist layer formed upon a blanketreflective conductor layer, the method of the present invention willalso in general attenuate standing wave reflections from surfaces ofreflective layers employed within microelectronics fabricationsindependent of the presence or absence of a photoresist layer formedupon the reflective layer.

Referring now to FIG. 3, there is shown a schematic cross-sectionaldiagram of an integrated circuit microelectronics fabrication withinwhich there is attenuated an inhomogeneous standing wave photoexposurewithin a blanket photoresist layer formed over a blanket reflectiveconductor layer in accord with a preferred embodiment of a method inaccord with the present invention.

Shown in FIG. 3 is a substrate 20 having formed thereover a blanketreflective conductor layer 22. The blanket reflective conductor layer 22in turn has formed thereupon a blanket birefringent material layer 24.Finally, the blanket birefringent material layer 24 has formed thereupona blanket positive photoresist layer 26.

Although semiconductor substrates are known in the art of integratedcircuit microelectronics fabrication with either dopant polarity,several dopant concentrations and various crystallographic orientations,for the preferred embodiment of the method of the present invention, thesubstrate 20 preferably comprises a (100) silicon semiconductorsubstrate having a N- or P-doping. The substrate 20 also preferablycomprises several other conductor layers, semiconductor layers and/ordielectric layers which are typically formed upon semiconductorsubstrates employed in forming integrated circuit microelectronicsfabrications. Although not specifically illustrated in FIG. 3, thesubstrate 20 also preferably comprises formed therein and/or thereuponelectrical circuit elements, such as but not limited to transistors,resistors, capacitors and diodes, which are also similarlyconventionally employed within integrated circuit microelectronicsfabrications.

Similarly, although it is also known in the art of integrated circuitmicroelectronics fabrication that conductor layers may be formed throughmethods and materials including but not limited to thermally assistedevaporation methods, electron beam assisted evaporation methods,chemical vapor deposition (CVD) methods and physical vapor deposition(PVD) sputtering methods through which may be formed conductor layers ofconductor materials including but not limited to metals, metal alloys,highly doped polysilicon and polycides (highly doped polysilicon-metalsilicide stacks), for the preferred embodiment of the method of thepresent invention the blanket reflective conductor layer 22 is typicallyand preferably formed at least in part of an aluminum containingconductor material, as is most common in the art of integrated circuitmicroelectronics fabrication. Typically and preferably, the blanketreflective conductor layer 22 is formed to a thickness of from about2000 to about 10000 angstroms. Typically and preferably, the blanketreflective conductor layer 22 has a reflectivity of greater than about50 percent at a wavelength of an actinic photoexposure radiation beamsubsequently employed in photoexposing the blanket photoresist layer 26.

In addition, while it is also known in the art of integrated circuitmicroelectronics fabrication that photoresist layers may be formed fromany of several photoresist materials chosen from the general groups ofphotoresist materials including but not limited to positive photoresistmaterials and negative photoresist materials, the preferred embodimentof the method of the present invention illustrates the method of thepresent invention practiced employing the blanket photoresist layer 26formed of a positive photoresist material. Functionally equivalentstructures may, however, also be formed in accord with the method of thepresent invention when employing a blanket photoresist layer, such asthe blanket photoresist layer 26, formed of a negative photoresistmaterial. Preferably, the blanket photoresist layer 26 is formed to athickness of from about 8000 to about 19000 angstroms.

Also shown in FIG. 3 is a photoexposure reticle 28 positioned above theblanket photoresist layer 26, and an actinic photoexposure radiationbeam 30 photoexposing a portion of the blanket photoresist layer 26exposed through the photoexposure reticle 28. In contrast with theblanket photoresist layer 14 a portion of which is photoexposed with theactinic photoexposure radiation beam 18 through a method conventional inthe art of microelectronics fabrication as illustrated in FIG. 1 andFIG. 2, there is substantially attenuated within FIG. 3 reflection ofthe actinic photoexposure radiation beam 30 back into to blanketphotoresist layer 26 from the blanket reflective conductor layer 22, dueto the presence within FIG. 3 of the birefringent material layer 24.Thus, within the preferred embodiment of the method of the presentinvention there is attenuated a standing wave photoexposure of theblanket photoresist layer 26.

In order to provide optimal performance of the method of the presentinvention, there are several parameters pertaining to the structurewhose schematic cross-sectional diagram is illustrated in FIG. 3, and inparticular to the blanket birefringent material layer 24 within thestructure whose schematic cross-sectional diagram is illustrated in FIG.3, for which parameters there are limits which are preferablycontrolled. In that regard, within the preferred embodiment of themethod of the present invention, the blanket birefringent material layer24 is chosen to exhibit a birefringence in a plane perpendicular to az-direction plane of the actinic photoexposure radiation beam 30 asillustrated in FIG. 3. Thus, the blanket birefringent material layer 24has a first real index of refraction in an x-direction planeperpendicular to the z-direction plane, the first real index ofrefraction being denoted as n_(bx), and the blanket birefringentmaterial layer 24 also has a second real index of refraction in ay-direction plane perpendicular to both the x-direction plane and thez-direction plane, the second real index of refraction being denoted asn_(by). Preferably, the maximum difference in the first real index ofrefraction of the material from which is formed the blanket birefringentmaterial layer 24 in the x-direction plane perpendicular to thez-direction plane, n_(bx), and the second real index of refraction ofthe material from which is formed the blanket birefringent materiallayer 24 in the y-direction plane perpendicular to the x-direction planeand the z-direction plane, n_(by), is preferably greater than about 0.1.Similarly, for the preferred embodiment of the method of the presentinvention the actinic photoexposure radiation beam 30 is formed ofcircularly polarized light, as is common within microelectronicsfabrication. Finally, it is also preferred within the method of thepresent invention that a thickness L_(b) of the blanket birefringentmaterial layer 24 is approximately equal to the quantity 1/4 |(λ/(n_(bx)-n_(by)))|, where λ equals the wavelength of the actinic photoexposureradiation beam 30, although the method of the present invention willstill provide value in attenuating a standing wave photoexposure of aphotoresist layer, such as the blanket photoresist layer 26, when thethickness L_(b) of the blanket birefringent material layer 24 is withina range of from about 1/8 |(λ/(n_(bx) -n_(by)))| to about 3/8|(λ/(n_(bx) -n_(by)))|.

Referring now to FIG. 4, there is shown a schematic cross-sectionaldiagram illustrating the results of further processing of the integratedcircuit microelectronics fabrication whose schematic cross-sectionaldiagram is illustrated in FIG. 3. Shown in FIG. 4 is a schematiccross-sectional diagram of an integrated circuit microelectronicsfabrication otherwise equivalent to the integrated circuitmicroelectronics fabrication whose schematic cross-sectional diagram isillustrated in FIG. 3, but wherein the blanket photoresist layer 26after having been photoexposed through the photoexposure reticle 28 withthe actinic photoexposure radiation beam 30 has been developed to formthe patterned photoresist layers 26a and 26b formed upon the blanketbirefringent material layer 24. In contrast with the standing wavephotoexposed patterned photoresist layers 14a and 14b formed upon theblanket reflective layer 12 through the method conventional in the artof microelectronics fabrication as illustrated in FIG. 2, the patternedphotoresist layers 26a and 26b formed upon the blanket birefringentmaterial layer 24 and over the blanket reflective conductor layer 22 asillustrated in FIG. 4 are formed with straight sidewalls rather thanirregular sidewalls.

Referring now to FIG. 5, there is shown a schematic cross-sectionaldiagram illustrating the results of further processing of the integratedcircuit microelectronics fabrication whose schematic cross-sectionaldiagram is illustrated in FIG. 4. Shown in FIG. 5 is a schematiccross-sectional diagram of an integrated circuit microelectronicsfabrication corresponding with the integrated circuit microelectronicsfabrication whose schematic cross-sectional diagram is illustrated inFIG. 4, but wherein there has sequentially: (1) been formed from theblanket birefringent material layer 24 the patterned birefringentmaterial layers 24a and 24b; and (2) been formed from the blanketreflective conductor layer 22 the patterned reflective conductor layers22a and 22b, through etching within a plasma 32 while employing thepatterned photoresist layers 26a and 26b as patterned photoresist etchmask layers. Within the preferred embodiment of the method of thepresent invention, the plasma 32 preferably employs an etchant gascomposition, or a sequence of etchant gas compositions, appropriate tothe materials from which are formed the blanket birefringent materiallayer 24 and the blanket reflective conductor layer 22. As isillustrated in FIG. 5, the patterned birefringent material layers 24aand 24b and the patterned reflective conductor layers 22a and 22b areformed with dimensional integrity and straight sidewalls since thepatterned photoresist layers 26a and 26b are formed with an attenuatedstanding wave photoexposure, thus yielding patterned photoresist layerswith straight sidewalls.

As is understood by a person skilled in the art the patternedphotoresist layers 26a and 26b and the patterned birefringent materiallayers 24a and 24b may be subsequently stripped from the integratedcircuit microelectronics fabrication whose schematic cross-sectionaldiagram is illustrated in FIG. 5 to yield an integrated circuitmicroelectronics fabrication which may subsequently be fabricated tocompletion with additional layers and structures formed through methodsand materials as are conventional in the art of integrated circuitmicroelectronics fabrication.

EXAMPLE

The following is a prophetic example through which there is calculatedactinic photoexposure radiation power as a function of depth z withinthe z-direction (ie: P (z)) within a photoresist layer formed upon abirefringent material layer which in turn is formed upon a reflectiveconductor layer in accord with the preferred embodiment of the method ofthe present invention.

Within the prophetic example, the reflective conductor layer, whichcorresponds with the blanket reflective conductor layer 22 asillustrated in FIG. 3, has a complex index of refraction n₄ ' whichequals a difference between a real index of refraction n₄ and animaginary index of refraction K₄ (ie: n₄ '=n₄ -jκ₄), where j equals √-1.The reflective conductor layer also has a permittivity ε₄ and apermeability μ₄. Similarly, within the prophetic example, thebirefringent material layer, which corresponds with the blanketbirefringent material layer 24 as illustrated in FIG. 3, has: (1) acomplex index of refraction in the x-direction n_(3x) ' which equals adifference between a real index of refraction in the x-direction n_(3x)and an imaginary index of refraction in the x-direction κ_(3x) (ie:n_(3x) '=n_(3x) -jκ_(3x)); and (2) a complex index of refraction in they-direction n_(3y) ' which equals a difference between a real index ofrefraction in the y-direction n_(3y) and an imaginary index ofrefraction in the y-direction κ_(3y) (ie: n_(3y) '=n_(3y) -jκ_(3y)). Thebirefringent material layer also has a permittivity ε₃ and apermeability μ₃. In addition, within the prophetic example, thephotoresist layer, which corresponds with the blanket photoresist layer26 as illustrated in FIG. 3, has a complex index of refraction n₂ 'which equals a difference between a real index of refraction n₂ and animaginary index of refraction κ₂ (ie: n₂ '=n₂ -jκ₂). The photoresistlayer also has a permittivity ε₂ and a permeability μ₂. Finally, withinthe prophetic example, an actinic photoexposure radiation beam, whichcorresponds with the actinic photoexposure radiation beam 30 asillustrated in FIG. 3, travels through air when impinging upon thephotoresist layer, where air has a complex index of refraction n₁ 'which equals a difference between a real index of refraction n₁ plus animaginary index of refraction κ₁ (ie: n₁ '=n₁ -jκ₁). Air also has apermittivity ε₁ and a permeability μ₁.

Within the prophetic example, the thickness of the birefringent layer isdenoted as L_(b) and the thickness of the photoresist layer is denotedas L_(p). The thickness of the reflective conductor layer is assumed tobe finite and therefore also assumed to be semi-infinite. In addition,within the prophetic example, the wavelength of the actinicphotoexposure radiation beam is denoted as λ and the actinicphotoexposure radiation beam is assumed to have a normal incidence tothe photoresist layer. Similarly, within the prophetic example, thereexists: (1) a reflection coefficient of the actinic photoexposureradiation beam from within the photoresist layer at the air-photoresistlayer interface, denoted as r₂₁ ; (2) an effective reflectioncoefficient of the actinic photoexposure radiation beam from within thephotoresist layer in the x-direction at the photoresistlayer-birefringent material layer interface, denoted as reff_(23x) ; (3)an effective reflection coefficient of the actinic photoexposureradiation beam from within the photoresist layer in the y-direction atthe photoresist layer-birefringent material layer interface, denoted asreff_(23y) ; and (4) a transmission coefficient of the actinicphotoexposure radiation beam into the photoresist layer at theair-photoresist material layer interface, denoted as t₁₂.

In the process of calculating the actinic photoexposure radiation beampower within the photoresist layer as a function of distance z withinthe z-direction within the photoresist layer there is first determinedan intrinsic optical impedance η_(i) for each of air, the photoresistlayer, the birefringent material layer and the reflective conductorlayer, in accord with equation 1,

    η.sub.i =√(μ.sub.i /ε.sub.i)=cμ.sub.i /n.sub.i '(1)

where η_(i) equals the intrinsic optical impedance of the pertinentmaterial, μ_(i) equals the permeability of the pertinent material, ε_(i)equals the permittivity of the pertinent material and c equals the speedof light in free space.

There is then also calculated: (1) the wavenumber of the actinicphotoexposure radiation beam within the within the photoresist layer,denoted as k₂ ; (2) the wavenumber of the actinic photoexposureradiation beam in the x-direction within the birefringent materiallayer, denoted as k_(3x) ; and, (3) the wavenumber of the actinicphotoexposure radiation beam in the y-direction within the birefringentmaterial layer, denoted as k_(3y), in accord with equations 2, equation3 or equation 4.

    k.sub.2 =2πn.sub.2 '/λ                           (2)

    k.sub.3x =2πn.sub.3x '/λ                         (3)

    k.sub.3y =2πn.sub.3x '/λ                         (4)

There is then also calculated the optical impedance at the photoresistlayer-birefringent material layer interface as determined for theactinic photoexposure radiation beam incident in the positivez-direction. The optical impedance at the photoresist layer-birefringentmaterial layer interface is determined, looking into the positivez-direction for x-polarized light, and denoted as Z_(3x), in accord withequation 5. The optical impedance at the photoresist layer-birefringentmaterial layer interface is also determined, looking into the positivez-direction for y-polarized light, and denoted as Z_(3y), in accord withequation 6.

    Z.sub.3x =η.sub.3x ((η.sub.4 +jη.sub.3x tan(k.sub.3x L.sub.b))/(η.sub.3x +jη.sub.4 tan(k.sub.3x L.sub.b)))(5)

    Z.sub.3y =η.sub.3y ((η.sub.4 +jη.sub.3y tan(k.sub.3y L.sub.b))/(η.sub.3y +jη.sub.4 tan(k.sub.3y L.sub.b)))(6)

There is then calculated: (1) the reflection coefficient of the actinicphotoexposure radiation beam from within the photoresist layer at theair-photoresist layer interface, denoted as r₂₁ ; (2) the effectivereflection coefficient of the actinic photoexposure radiation beam fromwithin the photoresist layer in the x-direction at the photoresistlayer-birefringent material layer interface, denoted as reff_(23x) ; (3)the effective reflection coefficient of the actinic photoexposureradiation beam from within the photoresist layer in the y-direction atthe photoresist layer-birefringent material layer interface, denoted asreff_(23y) ; and (4) the transmission coefficient of the actinicphotoexposure radiation beam into the photoresist layer at theair-photoresist material layer interface, denoted as t₁₂, in accord withequation 7, equation 8, equation 9 or equation 10.

    reff.sub.23x =(Z.sub.3x -η.sub.2)/(Z.sub.3x +η.sub.2)(7)

    reff.sub.23y =(Z.sub.3y -η.sub.2)/(Z.sub.3y +η.sub.2)(8)

    r.sub.21 =(η.sub.1 -η.sub.2)/(η.sub.1 +η.sub.2)(9)

    t.sub.12 =2η.sub.2 /(η.sub.1 +η.sub.2)         (10)

Assuming that the incident photoexposure light is circularly polarizedright handed, the electric field amplitude of the actinic photoexposureradiation beam in the x-direction at a distance z within the z-directionof the photoresist layer at time t=0, denoted as E_(x) (z,t), iscalculated in accord with equation 11 and the electric field amplitudeof the actinic photoexposure radiation beam in the y-direction at adistance z within the z-direction of the photoresist layer at time t=0,denoted as E_(y) (z,t), is calculated in accord with equation 12. Withinequation 11 and equation 12, E₀ ' equals the complex electric fieldamplitude of the incident actinic photoexposure light radiation beam (Reand Im are the real and imaginary parts thereof) and m equals an integer(ie: m=0, 1, 2 . . . ).

    E.sub.x (z,t=0)=Re{E.sub.0 '[(.sub.m=0,∞ Σt.sub.12 exp(-jk.sub.2 z)(r.sub.21 reff.sub.23x exp(-2jk.sub.2 L.sub.p)).sup.m)+(.sub.m=0,∞ Σt.sub.12 reff.sub.23x

    exp(-jk.sub.2 (2L.sub.p -z))(r.sub.21 reff.sub.23x exp(-2jk.sub.2 L.sub.p)).sup.m)]}=Re{E.sub.0 't.sub.12 (exp(-jk.sub.2 z)+reff.sub.23x exp(-jk.sub.2 (2L.sub.p -z))/(1-r.sub.21 reff.sub.23x exp(-2jk.sub.2 L.sub.p))}                                                (11)

    E.sub.y (z,t=0)=Im{-jE.sub.0 't.sub.12 (exp(-jk.sub.2 z)+reff.sub.23y exp(-jk.sub.2 (2L.sub.p -z))/(1-r.sub.21 reff.sub.23y exp(-2jk.sub.2 L.sub.p))}                                                (12)

The actinic photoexposure radiation power at a distance z in thez-direction within the photoresist layer is related to the foregoingamplitudes of the electric fields at the distance z in the z-directionwithin the photoresist layer by equation 13.

    P(z,t)∝E.sub.x.sup.2 (z,t)+E.sub.y.sup.2 (z,t)      (13)

Shown in FIG. 6 is a graph of actinic photoexposure radiation power as afunction of distance z within the z-direction of the photoresist layer.Within the calculation there has been assumed: (1) air at a real indexof refraction n₁ of 1, an imaginary index of refraction κ₁ of 0, apermittivity ε₁ of 8.854E-12 F/m (equal to ε₀) and a permeability μ₁ of4πE-7 H/m (equal to μ₀); (2) the photoresist layer having a real indexof refraction n₂ of 1.61, an imaginary index of refraction κ₂ of 0.0227,a permittivity ε₂ of (2.5916-0.0731j)ε₀ and a permeability μ₂ of μ₀ ;(3) a calcite birefringent material layer having a real index ofrefraction in the x-direction n_(3x), of 1.493, an imaginary index ofrefraction in the x-direction κ_(3x) of 0, a real index of refraction inthe y-direction n_(3y) of 1.673, an imaginary index of refraction in they-direction κ_(3y) of 0, a permittivity ε₃ of 2.7989ε₀ and apermeability μ₃ of μ₀ ; and (4) a reflective conductor layer having areal index of refraction n₄ of 1.27, an imaginary index of refraction κ₄of 1.95, a permittivity ε₄ of (-2.1896-4.9530j)ε₀ (calculated as ε₄ =ε₀(n₄)²) and a permeability μ₄ of μ₀.

The calculation employed in providing the graph of FIG. 6 also assumed athickness of the photoresist layer of 1.075 microns and an actinicphotoexposure radiation beam wavelength λ of 365 nanometers. Finally,the calculation also employed a thickness of the calcite birefringentmaterial layer L_(b) =1/4 |(λ/(n_(3x) -n_(3y)))|, although calculationsemploying a thickness of the birefringent material layer between about1/8 and about 3/8 times the quantity of |(λ/(n_(3x) -n_(3y)))| alsoprovide graphs illustrating similar advantages to the advantages asillustrated within the graph of FIG. 6.

As shown in the graph of FIG. 6, there is a curve 40 which correspondswith the optical power of the actinic photoexposure radiation beam as afunction of distance z within the z-direction of the photoresist layerwithout the presence of the birefringent material layer. Similarly,there is also shown in the graph of FIG. 6 a curve 42 which correspondswith the optical power of the actinic photoexposure radiation beam as afunction of distance z within the z-direction of the photoresist layerwith the presence of the birefringent material layer. As is seen throughcomparison of the curve 40 with the curve 42, there is obtained throughthe method of the present invention a substantial attenuation of astanding wave photoexposure of the photoresist layer with the actinicphotoexposure radiation beam by forming interposed between thephotoresist layer and the reflective conductor layer the birefringentmaterial layer in accord with the method of the present invention.

Although not particularly common in the art of microelectronicsfabrication, methods through which birefringent layers may be formedwithin other thin film fabrications, such as but not limited to thinfilm magnetic memories and liquid crystal displays, have been disclosedin the pertinent arts. See, for example, Shiraishi et al., "Fabricationof Spatial Walk-Off Polarizing Films by Oblique Deposition," IEEEJournal on Quantum Electronics, vol. 30(10), October 1994, pp. 2417-20.Such novel methods are not precluded for use within microelectronicsfabrications.

Specifically, Shiraishi et al. disclose that birefringent layers areknown to be formed from calcite and rutile crystal materials. Inaddition, Shiraishi et al. also disclose an oblique deposition methodwhich may be employed for forming birefringent material layers. Theoblique deposition method provides birefringent material layers whichare formed of slanted micro-columns of higher index of refractionmaterials (preferably of index of refraction greater than about 2) whichare separated by micro-voids (which typically have an index ofrefraction of about 1). Specific examples of such obliquely depositedbirefringent material layers which have been reduced to practice employmicro-columns formed of tantalum oxide, although prophetic examplesemploying micro-columns formed of silicon are also disclosed.

What is claimed is:
 1. A microelectronics fabrication comprising:asubstrate employed within a microelectronics fabrication; a reflectivelayer formed upon the substrate; a birefringent material layer formedupon the reflective layer; and a photoresist layer formed upon thebirefringent material layer.
 2. The microelectronics fabrication ofclaim 1 wherein the microelectronics fabrication is chosen from thegroup of microelectronics fabrications consisting of integrated circuitmicroelectronics fabrications, solar cell microelectronics fabrications,ceramic packaging microelectronics fabrications and flat panel displaymicroelectronics fabrications.
 3. The microelectronics fabrication ofclaim 1 wherein the reflective layer is chosen from the group ofreflective layers consisting of reflective conductor layers, reflectivesemiconductor layers and reflective dielectric layers.
 4. Themicroelectronics fabrication of claim 1 wherein the birefringentmaterial layer has a thickness of from 1/8 to 3/8 the quantity |λ/(n_(x)-n_(y))|, wherein:λ equals a wavelength of light whose standing wavereflection is attenuated in a z-direction orthogonal to the reflectivelayer; n_(x) equals a real index of refraction of the birefringentmaterial layer in an x-direction orthogonal to the z-direction; andn_(y) equals a real index of refraction of the birefringent materiallayer in a y-direction orthogonal to the z-direction and thex-direction.
 5. The microelectronics fabrication of claim 4 wherein thewavelength of light is a wavelength of circularly polarized light. 6.The microelectronics fabrication of claim 1 wherein the birefringentmaterial layer is a single component birefringent material layer.